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Central Asia’s Desertification

The Hangay Mountains of central Mongolia today serve as a large topographic barrier blocking moisture from reaching the Gobi Desert and interior Asia. Stanford doctoral candidate Jeremy Kesner Caves examined the uplift of the Hangay in the early Neogene, which may have helped to initiate aridification of interior Asia. (CREDIT: Jeremy Caves)

New Study Paints More Nuanced Picture of Central Asia’s Desertification

Written by AZoCleantech

A new study chronicles how central Asia dried out over the last 23 million years into one of the most arid regions on the planet. The findings illustrate the dramatic climatic shifts wrought by the ponderous rise of new mountain ranges over geologic time.

Researchers have long cited the uplift of the Tibetan Plateau and the Himalayan Mountains around 50 million years ago for blocking rain clouds’ entry into central Asia from the south, killing off much of the region’s plant life.

The new study, published online in the journal Geology, paints a more nuanced picture of Central Asia’s desertification. It suggests that the relatively recent rise of lesser-known mountain ranges, such as the Tian Shan and the Altai, further sealed off moisture from the west and north. As a result, great stretches of what we now consider western China, southwestern Mongolia and eastern Tajikistan became barren earth or laced by sand dunes.

“While Central Asia was probably never lush and verdant, it was certainly greener 23 million years ago and probably even greener in the more distant past,” said Jeremy Kesner Caves, the lead author of the study and a doctoral student at Stanford’s School of Earth, Energy & Environmental Sciences.

“One way to think about this change is that when viewed from space today, Central Asia appears very brown because of its expansive deserts,” Caves said. “If viewed from space 23 million years ago, though, Central Asia would have looked somewhat darker, simply due to there being considerably more leaves and vegetation.”

Reading carbon

Caves and his co-authors arrived at their conclusions after measuring the carbon isotope values in buried, ancient soil samples. A particular isotope, or version, of carbon found in the samples speaks to the dryness of conditions at the time of the soil’s deposition. Wetter, rainier conditions allow for greater numbers of organisms, including plants and soil-dwelling bacteria, to thrive and pull carbon out of their surroundings to fuel their growth and metabolism, leaving telltale carbon isotopes in their environment.